AngularJS 数字过滤器 fractionSize 限制为 20 位小数

Question

为什么 AngularJS 中的数字过滤器 fractionSize 限制为小数点后 20 位？

Distance1<span ng-model='distance'>{{distance| number:20}}</span> <br />

输出

1.00000000000000000000

但是

Distance2<span ng-model='distance'>{{distance| number:21}}</span> <br />

产出

NaN.000000000000000000000

var app = angular.module('myModule', []);
app.controller('myController', ['$scope', function($scope) {
  $scope.distance = 1;
}]);

span {
  padding: 3px;
  margin: 12px;
  background: yellow;
}

<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.2.23/angular.min.js"></script>
<div ng-app='myModule' ng-controller='myController'>
  Distance1<span ng-model='distance'>{{distance| number:20}}</span> <br />
  Distance2<span ng-model='distance'>{{distance| number:21}}</span> <br />
  </div>

Answer 1

原猜测

虽然我无法在数字过滤器的 source, I'm guessing somewhere deeper it is utilizing Number.toFixed which is limited to 20 decimal spaces. Per the MDN documentation 中找到参考：

The number of digits to appear after the decimal point; this may be a value between 0 and 20, inclusive, and implementations may optionally support a larger range of values. If this argument is omitted, it is treated as 0

更好的猜测

我做了一些测试，我认为这是最大长度为 20 的 Number.prototype.toFixed 的限制加上过滤器 source 中有 var MAX_DIGITS = 22 的事实的组合.我运行以下测试来检验我的理论：

var $number = angular.injector().get('numberFilter')
$number(1, 20) // 1.00000000000000000000, 22 total chars
$number(1, 21) // NaN.000000000000000000000, 23 total chars (assuming if NaN evaluated to a single char)
$number(10, 20) // NaN.00000000000000000000
$number(10, 19) // 10.0000000000000000000

所以大家可以看到，22并不是指实际的数值，好像是指字符串的长度。仍然不清楚它如何处理 $number(0, 21) 而不是输出 NaN 字符串。

AngularJS 数字过滤器 fractionSize 限制为 20 位小数

AngularJS number filter fractionSize limited to 20 decimal places

angularjs

angularjs-filter

原猜测

更好的猜测